Purpose: To compare the performance of the 3M MLS II for the release of UHT products with traditional microbial method and pH measurement
Methods: Three flavors of whole fluid milk (UHT processed & aseptically filled) were inoculated with four microorganisms (B. subtilis, E. faecalis, P. aeruginosa, B. megaterium) at each of 3 inoculation levels (low, < 10 CFU/brick; high, 10-50 CFU/brick; control, no inoculation). Samples (n = 30) were analyzed for each flavor-microorganism combination following incubation for 72h at 30°C, using the MLS, streaking on nutritive agar and pH measurement
Results: For all flavors analyzed, MLS correctly detected 100% of samples with both high and low levels of inoculums of B. subtilis and P. aeruginosa, using streaking on nutritive agar as a comparison. At both high and low levels of E. faecalis, MLS correctly detected 71-100% of samples tested, using streaking on nutritive agar as a comparison. Interestingly, the pH method, widely considered to be an acceptable means of determining UHT sterility, correctly detected inoculated UHT product for 6-26% of those samples tested; only chocolate UHT milk with low-level E. faecalis was correctly detected for all samples. These results demonstrate that, particularly for lactose non-fermenting organisms, MLS provides a more accurate means of detecting contamination of UHT dairy products
Significance: For the UHT flavored whole milk (strawberry, cookies and cream, chocolate), the MLS demonstrated comparable results to the reference methods for the rapid detection of contaminated UHT bricks in as little as 72 hours of incubation.